Jack Straw has confirmed he will join the BNP leader Nick Griffin on an edition of the BBC's Question Time programme.

Labour had previously made a point of not appearing alongside the far-right party, but Straw said today that he was "delighted" to have the opportunity to take on Griffin, MEP for the North West, on the flagship programme.

Anti-fascist campaigners reacted with anger to the news and called for huge demonstrations to be mounted outside the BBC studios when the programme is made.

Straw, who regularly takes on all comers in debate from a soapbox in his Blackburn constituency, said the BNP were defeated when Labour "fought them hard". He told the BBC's Politics Show North West: "Some people support the BNP because they subscribe to their views. Others do it out of a feeling of despair. We've got to make the argument, and I'm delighted to do so."

The BBC confirmed that the two men were among the panellists booked for a recording of the show, hosted by David Dimbleby, in London on 22 October. The Conservatives and Liberal Democrats confirmed that they would be fielding representatives.

Straw's announcement brought a renewed attack on the BBC's decision from his cabinet colleague, Peter Hain. The Welsh secretary said he was meeting BBC executives on Wednesday to try to persuade them to drop their decision to give the BNP a seat on the panel. He also questioned whether the BBC was legally obliged to invite the BNP to appear after the party won two seats in the European parliament elections in June and said he would back any legal action that challenged the decision.

"I don't buy this stuff that under electoral law the BNP's two European seats allows them to be treated in the same way as the mainstream parties. If there were to be any legal action against the BBC I would wish it well," said Hain.

He added: "Their [the BNP's] MEPs were elected on a tiny vote and a low turnout. It's an absolute scandal that the BBC are treating an avowedly racist and fascist [party] on equal terms, in a way that will legitimise their standing in the public's eyes."

Hain said he was directing his anger at the BBC, rather than Straw, saying the corporation had put Labour ministers in an "impossible position" because they did not want the BNP to go unchallenged by leaving an empty chair.

Unite Against Fascism has pledged to hold a demonstration against the BBC's decision. Hain said he fully supported the group's actions.

A BBC spokeswoman said its obligation to treat all parties registered with the Electoral Commission "with due impartiality" was enshrined in the corporation's charter. She said that by winning two seats in the European parliament the BNP had demonstrated evidence of electoral support at national level, which would be reflected in the coverage it received on programmes such as Question Time.

Tony Kearns, assistant general secretary of the Communication Workers' Union, said it was a "disgrace" that the BBC was offering the BNP a seat on Question Time despite a huge outcry in recent weeks. He called on ministers and MPs to join protests against the decision.

Gordon Brown announced earlier this month that Labour had agreed to field a minister against the BNP and said those with long-standing opposition to sharing a platform with the party would not come under pressure to appear, naming Hain, and the home secretary, Alan Johnson.

The Liberal Democrats said they will probably field Chris Huhne, their home affairs spokesman. The party's leader, Nick Clegg, said last week: "If the BBC ask one of these fascist thugs, who have been elected to the European parliament, on to one of their flagship programmes, then I want us to be there to take them on."

The Conservatives said they did not yet know who would represent them on the programme.